This invention relates to magnetic bubble propagation tracks for a magnetic bubble memory device, and more particularly to a magnetic bubble memory having ion-implanted propagation tracks with larger bias field operating margins.
Now, as a system for implementing the high storage density of magnetic bubble memory devices, ion-implanted propagation tracks, which was disclosed in U.S. Pat. No. 3,828,329, are being developed in various places. The ion-implanted tracks can easily be made because of their being gapless, and are suitable for implementing the high density of the device.
On the other hand, the magnetic bubble memory device has such an arrangement as shown in FIG. 1. A generator 1 generates magnetic bubbles, which are driven by a rotating field to be propagated to a major line 2 and further to minor loops 4 via swap gates 3, and the magnetic bubbles, as information, are stored in the minor loops 4. Next, the magnetic bubbles stored in the minor loops 4 propagate to replicators 5 by rotating field drive, and further to a detector 7 via a major line 6 so as to be read out as stored information.
In the magnetic bubble memory device constructed as shown in FIG. 1, however, it is not preferable to form the swap gates, replicators, transfer gates (not shown), etc., which serve to connect the major lines or a major loop with the minor loops, by ion-implanted elements. This is because, if they were made by ion-implanted elements, they would not perform their stabilized function. Thus, it has been proposed to form, with a soft magnetic material as usual, the swap gate, replicators, transfer gates, major lines (or major loops), and the parts of the minor loops in the neighborhood of the connection parts between the major lines (or major loops) and the minor loops, and to form the most parts of the minor loops by ion-implanted elements. The magnetic bubble memory device thus formed is called a "hybrid device". (See Japanese Patent Unexamined Publication No. 57-186,287.)
The details in the neighborhood of each replicator are shown in FIG. 2. In this figure, a major line 9 is made of soft magnetic materials 8, and bubbles are replicated by the current flowing through a conductor 11 arranged below a replicator 10. The part of a minor loop 12, in the neighborhood of the connection part with the major line 9, is made of the soft magnetic material 13, while most of the minor loop 12 is formed by ion-implanted elements 14. Such an arrangement contributes to high storage density of the chip to some extent since most of the minor loops, which occupy the chip of the magnetic bubble memory device for the most part, is formed by ion-implanted elements.
The magnetic bubble memory device as shown in FIGS. 1 and 2, however, does not allow unlimited miniaturization of each element in FIG. 2 in response to the need for the required higher density thereof.
This is because the elements 8, 10 and 13 made of soft magnetic materials, which have relatively larger dimensions, provide limited miniaturization in terms of their fabrication, and so the miniaturization of the ion-implanted elements only cannot meet the demand of the higher density of the device. There is also a limitation for the minimum sizes of the conductors 11, which are arranged below the swap gates, transfer gates and replicators all made of soft magnetic materials, since their electrical resistance must be lower than a predetermined value. Because of the limitation for the minimum sizes of the conductors, etc., the swap gates, transfer gates, and replicators, made of soft magnetic materials, must be of sizes larger than those of propagation paths made of a soft magnetic material.
Further, the miniaturization of the soft magnetic material elements results in reduction of a driving force for bubbles, which also provides a limitation for the minimum sizes thereof.
Since, for the reasons mentioned above, soft magnetic elements 8, 10, 13 and conductor 11 in FIG. 2 cannot be further miniaturized, ion-implanted elements 14 only can be further miniaturized. The miniaturization of only ion-implanted elements 14 can realize the further higher density in the longitudinal direction of FIG. 2. This, however, provides larger gaps between the adjacent minor loops, and so increased wasteful areas on the chip, which is an obstruction against the demand of realizing the higher density of the device.
Such an arrangement as shown in FIG. 3 has been proposed as a magnetic bubble memory device for solving the problem mentioned above. (See Digests of the 6th annual conference on Magnetics in Japan (1982, 11) 15 pD-7 (p. 84).) This, as apparent from the figure, intends to realize the higher density of the device by folding the minor loops a few times to relax the problem mentioned above.
The magnetic bubble memory device as shown in FIG. 3, like FIG. 1, is composed of a generator 1, a major line 2, swap gates 3, folded minor loops 4, replicators 5, a major line 6, and a detector 7. This system of device necessitates inside turns for each minor loop, designated by 20.
FIG. 4 shows an enlarged view of the inside turns, in which bubbles are transferred in the direction of an arrow 21, and are led in the direction of an arrow 22 via inside turn 23. Numeral 24 also designates the same inside turn as 23.
The inventors of this invention investigated the operating bias field margins of the bubbles in the neighborhood of the inside turns 23, 24 and found that they are extremely deteriorated as compared with the operating bias margins of straight propagation tracks 21, 22.
This means that the bubbles cannot stably propagate along the inside turns 23, 24, and so provides a serious problem in putting into the practical magnetic bubble memory devices with the minor loops folded several times.